In the past few decades a large number of publications concerned with gastric blood flow have appeared. The impetus for these studies has arisen largely from a consideration of the relationship between gastric blood flow and gastric acid secretion. Generally increased secretion and increased blood flow are associated findings. This association or possible interrelationship seems probable although disagreement still exists. Most investigations have been done under unphysiologic conditions and almost all studies have been concerned only with the secretory portions of the stomach. Distinction between the gastric antrum and the secretory portion of the stomach has been attempted only in a few instances with some evidence which indicates that flow to the antrum may be entirely independent of flow to the secretory portions of the stomach. Since the antrum is the major source of control of gastric secretory function, relationships between antral blood flow and known states of physiologic antral and gastric mucosal function should be of great importance. Recently the measurement of gastrin in serum has been made possible by the application of radioimmuno assay techniques. Specifically, antral mucosal blood flow and serum gastrin will be measured in the dog under conditions of fasting, gastrin release by application of acetylcholine to the antral mucosa, antral inhibition by acidification or atropinization of the antral mucosa. Effects of exogenous and HC1 stimulation with histamine and pentapeptide gastrin will also be determined. Mucosal blood flow measurements will be obtained repeatedly and sequentially in the same animal by use of the Krypton 85 isotopic decay technique introduced by Bell and Battersby and studied extensively in this laboratory.